I'm in the same boat. I haven't played actively enough to really get far. Since this event started I've gained about 40 or more levels just trying to get farming missions done thanks to a handy guide.
But I'm struggling to do Castle Retake so I can open another farming map.

I've CCed one archer, have a gold healer at 50 and most of the units I use are at level 30 now (and several at 50% affection). I've only finished the first two event missions, and I really don't think I'll be able to do anymore after the next two missions.
I really want to use Horus, the other one is nice to have but Horus is who I want.

So the only way to lower Unit cost and Skill up is from a future event?